AU8318898A - Water-sediment material property measurement device - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT WATER SEDIMENT MATERIAL PROPERTY MEASUREMENT DEVICE The following statement is a full description of this invention, including the best method of performing it known to me: r r o r *o \r

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This invention relates to the measurement of the physical properties of water-mud mixtures through the use of an acoustic device (the water-sediment material property measurement device, hereafter referred to as the "Mudlogger").

There is a need for a device which makes efficient measurements of the material properties of mixtures of water and sediment, or muds. The use of a device such as this ranges from environments such as mining tailings disposal ponds or other man-made pond structures, inland dams and water bodies and estuarine environments. The measurements needed include percent solids composition of the "mud", density and percent sand.

At this time, there are two methods of measuring the above parameters, direct and indirect.

Direct measurements involve taking physical samples of "muds" at different depths in the water column and analysing these samples physically and chemically in a laboratory to obtain the material properties listed above. Indirect measurements are where another property of the mud is examined, such as light penetration through the substance, and the -density or other physical properties are inferred from this measurement.

There are several existing systems which indirectly measure some of the properties of water sediment mixtures. These include optical systems (using light), and mechanical resonance systems, which measure changes in the resonance of a mechanical system and infer material properties from these resonance values.

A need exists for a more efficient, robust, low-cost indirect measurement system that can be used to derive the physical properties listed above. The "mudlogger" addresses this need. The mudlogger uses an acoustic technique for this indirect measurement. All earthly substances have the following acoustic properties: 1) acoustic velocity 2) acoustic attenuation and scattering properties The mudlogger measures these parameters in-situ (within the mud) through the use of the following components: a) Acoustic source sub-system b) Acoustic receiver sub-systems c) Signal processing and data display/storage subsystems d) mechanical rigging and cabling for the above systems This device achieves measurements of the above acoustic properties with the following technique. The acoustic source outputs a signal between 5 and 600 kHz (kilohertz) in frequency, either as a monofrequency pulse, a chirp (swept frequency) or as a monotone rn nl*- ~9~h llir (single frequency) signal. This signal is output from the source, and received by the two acoustic receivers (hydrophones). The source and two receivers are attached to the mechanical rigging, or "probe" which is inserted into the mud, as shown in figure 1. This signal from the source passses through the water-sediment mixture and is received first by the nearest receiver, and at a later time, is received by the second receiver. One key concept to this device is that the sound signal travels through the mud at a given velocity, creating a time delay of reception between the two receivers. Also, the sound that passes between these two receivers is changed, due to the acoustic scattering and absorption.

These key parameters are measured by the mudlogger system: 1) the acoustic velocity and 2) the change in the acoustic signal between the two receivers. These two key parameters can be linked to specific values of mud density, percent solids and percent sand, as described in the above section dealing with indirect measurement techniques.

Mudlogger sub-system description: a) Acoustic source sub-system The acoustic source sub-system is composed of a commercially purchased, underwater acoustic transducer or "pinger" and associated electronics, composed of i)Signal generation hardware (commercially purchased) S..:ii)Amplifier (commercially purchased) iii)cable from amplifier to transducer (commercially purchased) SThe signal generation hardware is composed of commercially available oscillators or other electronics that produces signals in the frequency band mentioned above. The amplifier amplifies this signal The Transducer takes the signal from the amplifier output cable and transforms this signal into a acoustic (sound) signal, which is transmitted into the sedimentwater mixture, and on to the receive electronics.

b) Acoustic receiver sub-systems The acoustic receiver sub-system is composed of the following: i)two receiver transducers (commercially purchased) ii)cable from the transducers to receive amplifiers (commercially purchased) iii)receive amplifiers (commercially purchased) The signal transmitted from the acoustic source passes through the sediment/water mixture and is received by the receive transducers, which convert the acoustic signal to an electronic signal This signal is passed through the electrical cables to the receive amplifiers which amplify the signals from the transducers.

c) Signal processing and data display/storage subsystems The signal processing and data display/storage sub-systems are composed of: i)electrical filters (commercially purchased) ii)data logger (commercially purchased) iii) laptop computer with proprietary software for data display and storage l-~I r r~- 3 The electrical filters will reduce unwanted noise components from the signal received from the receive transducer amplifier system. For example, if the system is utilising a acoustic frequency between 20 and 40 kHz, then the electrical filters would remove significant noise components outside this frequency band, eg- less than 20 kHz and greater than 40 kHz. A second set of filters reduces the signals to match the input to the datalogger (500Hz lowpass filter and rectifier) Next, these filtered signals from the two transducers are input into a data logger with sufficieni memory and throughput capacity to accomodate these two signals. One such datalogger is the Interworld Electronics (Melbourne) RAD 128 AID module/data logger. The output from this unit is input into a personal computer (laptop) through the serial port on the computer.

A Offshore Scientific processing routine, takes the data from the data logger and performs the following functions: 1) compares the two signals from two transducers 2) links this comparison with known values of percent sand, density, or percent solids 3) plots this inferred material property on the computer screen, and stores this data on the computer hard disc This process is repeated at different depths within the water/mud mixture in order to output a plot of density (or other physical property) with depth.

d) Mechanical rigging and cabling for the above systems The mechanical rigging for this system is composed of 1) Probe structure which transducers are attached to (manufactured to specification) 2) Electrical cables (commercially purchased) 3) Electronics enclosure to house fiters and dataloggers (commercially purchased) SThe probe structure is illustrated in figure 1, and is composed of a steel body with arms attached onto which the transducers are fixed to. This structure is lowered into and Sthrough the water/mud mixture as measurements are taking place. The cables connect the transducers to the electronics module at the surface (on a boat or other floating platform).

The electronics enclosure can be as simple as a wood box, or a sealed plastic or metal box/enclosure to house the electronics described above. The entire system is powered by either 240V ac power or a suitable DC power supply.

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Claims (4)

1. A method of indirectly measuring the physical properties of water/sediment mixtures utilising a single acoustic source and two acoustic receivers, where the difference in the signal (velocity and attenuation) received by two sensors is related to physical properties of the water/sediment mixture (percent solids, density and percent sand)

2. A mechanical probe device which the transducers are attached to, and lowered into the water/sediment mixture.

3. A system of electronic filters which conditions the signals from the receive transducers

4. Proprietary software which processes, displays and stores the indirectly measured physical property values. AN APPICANT 7 SEPTEMBER 1998 om: